Oxidation of two ternary Fe-Cu-5Al alloys in 1×10 5 Pa pure oxygen at 700 °C

Abstract

The oxidation of two two-phase ternary Fe-Cu-Al alloys containing about 5% Al(mole fraction), one Fe-rich and one Cu-rich, were studied at 700 °C in 1 × 10 5 Pa pure oxygen. The Fe-rich alloy (Fe-15Cu-5Al) shows two quasi-parabolic stages, with a large increase of the parabolic rate constant after about 4 h. The presence of 5% Al does not change greatly the oxidation rate of Fe-15Cu-5Al with respect to a binary Fe-Cu alloy of similar composition, which was quite different from the situation of the same alloys oxidized at 800 °C. Oxidation of Fe-15Cu-5Al at 700 °C produced an outer layer of iron oxides and an inner layer containing a mixture of copper metal, iron and aluminium oxide. On the contrary, the Cu-rich Fe-85Cu-5Al alloy presents a rather irregular kinetic behavior, with formation of an inner continuous alumina thin layer and a rather irregular outer layer. The outer layer with a rather irregular thickness was mainly composed of a matrix of copper oxides plus some aluminium and iron oxides presenting in the deep part of the layer at certain locations. As a result of the formation of a protective alumina layer, the presence of 5% Al greatly reduced the oxidation rate of Fe-85Cu-5Al with respect to a binary Fe-Cu alloy of similar composition, which was also quite different from the situation of the same alloys oxidized at 800 °C. Moreover, the oxidation rate at 700 °C of the Fe-85Cu-5Al alloy was much lower than that of Fe-15Cu-5Al alloy due to the same reason.˙